The colour of the teeth is influenced by a combination of their intrinsic colour and the presence of any extrinsic stains that may form on the tooth surface. Extrinsic colour is linked with the adsorption of materials into the acquired pellicle on the surface of enamel, which ultimately cause staining. Factors that influence extrinsic stain formation include poor tooth brushing technique, smoking, dietary intake of coloured foods (e.g. red wine), subject age and the use of certain cationic agents such as chlorhexidine or metal salts like tin and iron.
Consumers have always had a strong desire for white teeth and many individuals are dissatisfied with their current tooth colour. This desire for whiter teeth has given rise to a growing trend in the increased use of tooth whitening products.
Current whitening toothpastes rely on optimised abrasive and chemical components to maximise stain removal and prevention. During brushing, abrasive particles become temporarily trapped between the toothbrush and the stained tooth surface and abrade away the stain. Chemical components may also be used, usually in conjunction with abrasive particles, and include calcium chelators, polymers, surfactants, enzymes and oxidising agents.
EP 1 935 395 describes a novel optical approach to tooth whitening. On brushing with the toothpaste described in this publication, a blue pigment (in particular blue covarine) is deposited onto the tooth surface, where it is able to change the optical effects of the tooth surface, and enhance the measurement and perception of tooth whiteness. This toothpaste is intended to produce a temporary tooth whitening effect that can be reapplied as frequently as desired, as it contains no harsh chemicals, but is not intended to produce any permanent changes to the colour of the teeth.
The present inventors have now found that certain pearlescent pigments can produce superior temporary tooth whitening effects when used in a context similar to that described in EP 1 935 395.
US2005/0175552 and US2005/0287084 describe compositions for imparting whiteness to teeth, which may include various types of pearlescent particle. The compositions described are evaporative solvent-based systems intended for direct application to the teeth by adhesion or painting, after which they dry to form a film.